HILTOX A.SMITH AND BURCH B. STEWART
3808
[CONTRIBUTIONFROM
THE
DEPARTMENT O F CHEMISTRY, THEUXlVERSITY O P
Vvl. 82 'rENSESSEE
1
The Exchange of Deuterium with Methanol over Raney Nickel Catalyst and the Effect of Certain Nitro Compounds upon the Exchange BY HILTON A. SMITHAND BURCH13. STEWART RECEIVED JANUARY 26, 1960 Deuterium gas exchanges slowly with liquid methanol over Raney riickel catalyst at 35'. The reaction is zero order with respect to deuterium pressure and has a low activation energy. The influences of catalyst weight, catalyst treatment, and of the presence of certain nitro compounds have been studied. Since active Raney nickel can liberate hydrogen directly, a method for determining the origin of hydrogen which undergoes exchange with the deuterium gas has been developed. It has been shown t h a t the exchanged hydrogen does originate from the hydroxyl hydrogen of methanol. The results are discussed in the light of the mechanism of catalytic exchange and catalytic hydrogenation reactions.
The catalytic exchange of deuterium gas with alcohol vapors over various catalyst films has been reported previously.' Nickel catalyst was found to be the least active for the exchange. Several deuterium exchange reactions icvolving hydrogenation solvents and catalysts have been Since the kinetics for the hydrogenation of various nitro compounds in alcohol solvent using Raney nickel catalyst has been studied p r e v i ~ u s l ya, ~study of the catalytic deuterium exchange reactions for similar systems was undertaken to determine whether there are kinetic correlations and whether the mechanism could be better understood. Experimental Materials.-Raney nickel was prepared in several batches by a method described previously.6 Drum grade synthetic methanol was fractionally distilled in a n 8-foot Vigreux column, and constant-boiling cuts were collected at a reflux ratio of 10: 1. Nitrobenzene, aniline, nitroethane, nitroniesitylene, P-nitrostyrene and 2-nitro-I-butene were prepared and purified a s in earlier w0rk.~>7Deuterium gas was obtained from the Stuart Oxygen Co. Electrolytic hydrogen was obtained from the National Cylinder Gas Co. The deuterium and hydrogen were passed through a trap cooled with liquid nitrogen immediateIy before use. Heavy water of greater than 99.S7, purity was obtained from the Liquid Carbonic Co. Deuterated methanol was prepared by acid-catalyzed equilibrations of 25 ml. of methanol with four successive 25-mi. portions of heavy water each followed by slow fractional distillation. No hydrogen could be detected in the sample gas resulting after treating the heavy methanol with deuterium gas and Raney nickel catalyst. A minim u m purity of the CH30D of 99.5y0 may be calculated by use of the experimental value, 1.81, for the equilibrium constant of the reaction DzO CHIOH -+ CH30D f HOD.* Exchange Apparatus and Procedure.-The exchange apparatus and procedure were similar t o those described in previous work.3 Raney nickel while wet with methanol was added to the desired volume of methanol with a calibrated glass tube. After the exchange reaction was completed, the nickel was collected upon a tared fritted funnel under a n atmosphere of carbon dioxide, dried in a vacuum desiccator, and weighed under a carbon dioxide atmosphere.
+
(1) J. R . Anderson a n d C . Kemball, T Y Q ~ FXu.v a d a y Soc., 61, Of30 (1955). (2) H. A. S m i t h and E . L. McDaniel, THISJOURNAL, 77, 533 (1955). (3) L. E. Line, B. W y a t t a n d H. A. S m i t h , ibid., 74, 1808 (1932). (4) E. L. McDaniel a n d H. A. Smith, "Advances in Catalysis," Academic Press, Inc., New York, N. Y., 1957, Vol. I X , p. 70. ( 5 ) H. A. Smith a n d W . C . Bedoit in P. H. E m m e t t , "Catalysis," Reinhold Publishing Corp,, New York, K,Y . , 1955, Vol. 111, p. 149, ( G ) W. C . Bedoit, "Studies of R a n e y Nickel Catalysts," Master's Thesis, T h e University of Tennessee, 1948, Appendix. (7) H. A. Smith a n d W . C. Bedoit, J . Phys. Colloid Chein., 66, 1085 (1951). (8) H. K w a r t . L. P. K u h n and E . L. Bannister, THISJ O L J R K A I , , 76, 6948 (1954).
Analyses.-The analytical apparatus was simil:tr to t h a t described earlier.3 However, the effusioineter used to analyze hydrogen and deuterium incorporated it glass effusioii pinhole bulb which could be evacuated. h glass pinhole system for effusiometry has been described previously.gJ0 Effusions were carried out a t 35 =t0.2". Calculations were similar t o those in earlier work. When hydrogen may be liberated directly from the Ccttdlyst as well as by exchange with methanol, more data are required for a calculation of percentage exchange with the methanol. The difference in pressure readings before and after the exchange run was measured. The final reading will always be the sum of the initial deuterium pressure reading, and the increase in pressure due to hydrogen liberated from the catalyst itself. All readings were taken for the same volume and temperature. An expression for calculation of percentage exchange was derived ;C exchange = 100 = [100 =t4; H?] where
as defined previously3 PH2(1) is the increase i n pressure during the run, and P D z ( ,is ) the initial gas (deuterium) pressure.
Experimental Calculations and Results Preliminary experiments indicated that the rate of exchange of deuterium gas with methanol for a shaking rate of 270 cycles per minute was proportional to the weight of Raney nickel catalyst added, provided this did not exceed 300 nig. Therefore, all exchange measurements were made under these conditions, In general, the percentage exchange was determined three times under any set of experimental conditions, and the recorded values are the average of these. The percentage exchange per minute per unit weight of catalyst decreased linearly with an increase in initial deuterium pressure (total pressure less vapor pressure of methanol) as shown in Fig. 1. The order of the exchange reaction with respect to deuterium pressure is thus zero order, and it is pseudo zero order with respect to methanol concentration, since this material is present in considerable excess. Zero-order rate constants were calculated from the equation
where and PD,are the pressures of hydrogen and deuterium, t is the time, w is the weight of catalyst, and the percentage exchange is determined in (9) Atomic Energy Cummission Research Development R r p o r t . O.R.N,L.-2997, Series A , July lL4. 1956 (Declassified) (10) D. A. Lee, A?zai. C ; m n , SO, 1296 (1958)
EXCHANGE OF DEUTERIUM WITH METHANOL
Aug. 5, 1960
the effusion apparatus. Table I shows that the rate constants calculated in this manner agree reasonably well when deuterium pressures above 500 mm. are employed. Below this pressure there is probably insufficient deuterium present to maintain the surface coverage required for zero-order kinetic behavior. The zero-order constants in Table I should be corrected for the volume (53 ml.) of gas in the system in order to compare them with constants obtained in different systems. The value of the rate constant corrected in this manner becomes 2.91. mm. min.-lg.-lat 35".
12
-
10
-
* 1.
.-.s
I
hi
3899
86-
g
4-
TABLEI 0 400 800 1200 ZERO-ORDERRATE CONSTANTS FOR DEUTERIUM-METHANOL Initial deuterium pressure, mm. EXCHANGE OVERRANEYNICKELAT 35" Fig. 1.-The effect of initial deuterium pressure upon the P0,o h a ,b Catalyst wt., km, methanol-deuterium exchange reaction mm. min. -1 g. - 1 mm. mm. g. 323 403 507 76 1 799 897 181
85.2 97.9 49.8 122.5 119.9 76.3 77.3
0.232 ,220 ,096 ,200 .221 ,146 ,147
36.7 44.5 51.9 61.3 54.3 52.3 52.6 Av. 5 4 . 3 a Corrected for vapor pressure of methanol. *After 10 min. shaking time. Neglecting first two values.
The zero-order expression for the exchange reaction predicts a straight line when P His~plotted versus reaction time. Figure 2 shows that the plot is linear for the exchange to about &?yoreaction. The points represent individual runs for the given times. A single run cannot be followed analytically by the effusion method, since the gases are lost upon analysis. Exchange runs were carried out a t four temperatures to determine the apparent activation energy. A plot of log kl.0 versus 1/T is shown in Fig. 3. The apparent activation energy is 3500 cal. per mole. To ascertain whether only the hydroxyl hydrogen of methanol was involved for the exchange reactions, the following experiments were carried out. An exchange run using 10 ml. of heavy methanol (CH30D) and 53 ml. of deuterium gas a t 799 mm. for 10 minutes and a t 35" gave no detectable exchange. This is evidence that the hydrogen originates neither from the catalyst nor from the hydrogen atoms attached to the carbon of methanol. Another run using 10 ml. of heavy methanol (CH,OD) and 53 ml. of hydrogen gas a t 35" gave an exchange (9.99% exchange per gram per minute) which is comparable to that obtained using ordinary methanol with deuterium. Thus, it was concluded that only the hydroxyl hydrogen of methanol is involved in the exchange reaction with deuterium. Deuterium gas exhibits an average of 71.1y0exchange per grain of catalyst for 10 minutes using pure methanol. This value was adopted for the standard catalyst; see Table 11. Various concentrations of nitromesitylene, nitroethane, &nitrostyrene, nitrobenzene and 2-nitro-1-butene were used to determine their effect upon the deuteriummethanol exchange. The reactions were carried out for 10 minutes a t 35.0" with an initial deuterium pressure of 799 mrri. Catalyst weights were less
1tioo
t
1200
&
h
6
800 400
10
Fig. 2.--Zero-order
20 30 40 50 60 Time, min. plot for deuterium-methanol exchange.
3 30 3.40 103 eiiergy plot for deuterium-metha1101 exchange.
3.10
3.20
I/T
Fig. 3.-Activation
x
than 300 mg. in order to have equilibrium amounts for the shaking rates. Table I1 shows that the higher concentrations of all of the compounds except nitromesitylene prevented the exchange. The nitromesitylene solution gave a value for the percentage exchange almost equal to that obtained with pure methanol. There was no significant decrease for concentrations as great as 0.27 mole per liter. The mini-
3900
TADAAKI NAKABAYASHI
VOl. 82
mum may be due to poisoning of the catalyst by the small quantity of amine formed during the exchange, and the plateau a t higher concentrations may be due to appreciable adsorption of the nitro compound which would displace the amine.
versed] in that the reduction is zero order with respect to the hydrogen pressure and first order with respect to the acceptor. The exchange experiments with deuterium gas and acetic acid in the presence of platinum and with deuterium gas and methanol in the presence of TABLE I1 Raney nickel reflect these differences. In the first THEEXCHANGE O F DEUTERIUM GAS OVER RANEYNICKEL situation, aromatic nitro compounds when added in small quantities prevent the exchange,* while CATALYST WITH CERTAIN METHASOL SOLUTIONS 7c ex. g.?a Concn., mole/l. % ex. g. - l a Concn., rnole/l. aliphatic nitro compounds do For experi0 (pure MeOH) 71,lb p-Kitrostyrene ments with deuterium gas and methanol over Nitromesitylene 0.0129 47.8 nickel, both aliphatic and aromatic nitro compounds prevent the exchange. Thus, both hydrogenation 0.0134 40.4 ,0587 14.1 and exchange experiments indicate strong adsorp,0198 48.1 .097l 7.36 tion of both nitroparaffins and aromatic nitro com,0454 65.6 ,1553 0 pounds on the nickel surface. Presumably these, ,0454 63.7 ,2279 0 when present in appreciable concentrations, ex,0705 64.5 Piitrobenzene clude the methanol from the catalyst surface, thus ,0935 60.8 0,0257 17.7 preventing the exchange reaction. ,0992 57.5 ,0514 11.5 The situation occurring with nitromesitylene is .1674 60.8 0771 0 unusual, in that it does not prevent the exchange. ,2710 63.7 ,1285 0 It is well known that the methyl substituents pre,2710 67.2 2-Sitro-1 -butene vent resonance between the nitro group and the ,2710 63.2 0,0169 19.2 benzene ring, and this influences such properties as Sitroethane ,0338 0 0.0340 35.3 ,0676 0 dipole moments” and Raman spectra,’*thus making ,0680 19.4 the compound behave somewhat more as a nitroparaffin than as an aromatic nitro compound. This ,1020 4.34 is evidenced in the hydrogenation of nitromesitylene ,1360 0 over platinum in acetic acid solution.’ However, For 10 minutes reaction time. *Average of sevcn determinations, each representing three analyses. since nitroparaffins and aromatic nitro compounds influence the exchange of deuterium with methanol Discussion over Raney nickel, one would expect that the nitroThe kinetic behavior of the catalytic hydrogena- mesitylene would suppress the exchange reaction. tion of nitro compounds in ethanol solution over The reason for its behavior is not clear unless there Raney nickel catalyst is first order with respect to may be some unexpected exchange of deuterium hydrogen pressure and zero order with respect to with the nitromesitylene itself. the hydrogen acceptor. This is found for both Acknowledgment.-The authors are indebted to aromatic and aliphatic nitro compounds, and is in the United States Atomic Energy Commission for contrast to the behavior over platinum catalyst support of this work. with acetic acid solvent. In the latter case, the hy(11) F. Brown, J. 31. A. deBruyne a n d P. Gross, THISJ O U R X A L , 66, drogenation of the aromatic nitro compounds is also 1291 (1935). first order with respect to hydrogen pressure and (12) R. H. Saunders, M J. h l u r r a y a n d F.F. Cleveland, i b i d . , 63, zero order with respect to the nitro compound; 3121 (1941). but for nitroparaffins, the kinetic behavior is re- KNOXVILLE, TESS. 0
[CONTRIBUTION FROM THE CHEMICAL
LABORATORY, FAC~ZTY O F LIBERAL ARTS MIYAZAKI CITY, MIYAZAKI, JAPAX]
ASD EDUCATIOS, k 1 I Y A Z A K I USIVERSITY,
Studies on the Mechanism of Clemmensen Reduction. I. The Kinetics of Clemmensen Reduction of p-Hydroxyacetophenone BY TADAARI NAKABAYASHI* RECEIVED A ~ G U S 26, T 1959 The kinetics of the reduction of P-liydroxyacetoplierione with zinc amalgam and hydrochloric acid has been studied a t 60”. Except in t h e initial stage, t h e reaction is first order with respect t o t h e ketone. Chloride ion and zinc concentration have a predominant effect on t h e rate, whereas t h e effect of the potential of t h e zinc amalgam or hydrogen ion concent.ration is small. T h e effect of polyvinylalcohol on t h e r a t e and on the potential of zinc amalgam are reported. The apparent energy of activation of t h e reaction is 5.1 kcal./mole. A hypothesis on t h e mechanism of this reaction is presented.
Clemmensen reduction is widely employed in organic syntheses,l but the mechanism of the reac* D e p a r t m e n t of Industrial Chemistry, F a c u l t y of Engineering, Shinshu University, Nagano C i t y , N a g a n o , J a p a n . (1) E. L . l I a r t i n , “Organic Reactions,” vUi. I , edited b y R h d a r n s , John \Viley 8: Sons, Inc., New York, N. Y . , 1942, p . 155.
tion is not yet established. The present work has been undertaken in order to solve this problem. Steinkonf and Wolfram studied the Cleniineiisen reduction of benzophenone, acetophenone, esters of keto acids and benzaldehyde.’ The nlechanism ( 2 ) I\’. Strinkopf and A . Wolfram, :11in., 430, 113 (1923).
